Video display terminals are now commonplace as a result of the rapid increase in the use of computers and the like. The usual display surface of such a terminal is a cathode ray tube but other possible display surfaces include light emitting diodes (LED), liquid crystal diodes (LCD) or plasma display devices. Since the display surface of a terminal is usually relatively dark, it serves to reflect glare from the surrounding environment, hence reading of the information on the display surface can be difficult. This glare problem was to a large extent overcome by the addition of a glare filter as described in U.S. Pat. No. 4,253,737 issued to Patrick Brennan and Eric Thomson.
An equally and possibly more serious problem is the radiation of electromagnetic energy from the area of the display surface and the generation of static electrical field adjacent to the surface. Electromagnetic radiation is more likely to occur with the use of a cathode ray tube as a display surface; however static electrical fields can exist with other forms of display surfaces. While a good deal of attention has been directed toward the suppression of electromagnetic radiation, it has not been completely eliminated from unshielded cathode ray tubes and other display devices. Throughout this specification the display surface of the video display terminal will be most usually referred to as a cathode ray tube; however, it should be understood that the present invention is applicable to any form of display surface where glare and radiation can occur.
Currently electromagnetic radiation from the face of a cathode ray tube is reduced by the use of a conductive filter screen placed in front of the tube. The filter screen is connected electrically to the system ground of the cathode ray tube to conduct the radiation and any generated static electrical fields to the system ground and thus to reduce or eliminate the radiation from the face of the tube. These filter screens have also been formed or coated with glare reducing materials to reduce the reflection of surrounding light from the face of the tube.
Filter screens of the prior art type have been formed from woven fine yarn, wires or fibers to produce a mesh fabric of those fibers. The fabric is then cut and framed to the desired size and coated or impregnated with conductive and nonreflective materials as desired to form the filter screen for the face of a cathode ray tube. The fibers of the fabric should have a diameter in the 30 to 80 micron range, depending on whether the application is for color or black and white terminals. The color terminals have a finer dot pattern or pixcel dot size on the face of the cathode ray tube and therefore require a mesh designed for color displays and a more critical orientation of the fabric with respect to the face of the cathode ray tube. Typically the mesh needed for a display terminal filter screen is formed from fibers in the range of 0.001 inches (0.00254 centimeters) to 0.003 inches (0.00762 centimeters) diameter and a thread count of 75 to 300 fibers per inch. The limitation on the thread count of the mesh material is the limitation on the ability to form fibers of a smaller diameter, and the utility of the mesh for display terminal filter screens is the spacing between apertures in the mesh; that spacing being limited by the fiber size. The mesh formed by these fibers is typically then coated with a conductive coating and an anti-reflective color coating is then applied.
The production of mesh materials to the above specifications has been difficult and the cost of producing filter screens of such materials has been expensive. A method for forming suitable and desirable screen materials for the purpose above described at an increased rate and at a reduced cost has been needed.